Bats Host More Than 60 Human-Infecting Viruses

Below:

Next story in Science

Many animals harbor viruses that can jump to other species, but
bats may be in a class of their own when it comes to carrying
zoonotic (human-infecting) viruses. Bats are reservoirs for more
than 60 viruses that can infect humans, and host more viruses per
species than even rodents do, new research shows.

"There seems to be something different about bats in terms of
being able to host
zoonotic infections," study researcher David Hayman, a
wildlife epidemiologist at Colorado State University (CSU), told
LiveScience.

In recent years, bats have received a lot of attention for their
virus-hosting abilities. They've been shown to carry a number of
harmful infections, including rabies and viruses related to SARS
(severe acute respiratory syndrome). Moreover, research suggests
bats may be the original
hosts of nasty viruses such as Ebola and Nipah, which causes
deadly brain fevers in people.

This impressive track record left Hayman and his colleagues
wondering: Are bats somehow special in their ability to host
zoonotic viruses?

Bats vs. rodents

To find out, the researchers compared the virus-hosting abilities
of bats with those of rodents —which are also known to transmit
various zoonotic viral pathogens — by compiling and analyzing
databases of every virus identified in the animals. They found
that rodents host 179 viruses, 68 of which are zoonotic; bats, on
the other hand, harbor 61 zoonotic viruses, with 137 viruses in
total. Though rodents carry slightly more human-infecting
viruses, bats host more zoonotic viruses per species — on
average, each bat species hosts 1.79 zoonotic viruses, compared
with rodents' 1.48 viruses per species. [ 10
Deadly Diseases That Hopped Across Species ]

"It doesn't seem like a lot," said study co-author Angie Luis, a
CSU disease ecologist. "But when you consider that there are
twice as many rodent species as there are bat species, it's
highly significant."

The researchers also looked at different factors that could help
explain bats' surprising zoonotic viral richness. One factor
stood out: sympatry, in which multiple species of an order of
organisms inhabit the same geographical area. Bat and rodent
species were more likely to host multiple viruses if their
habitat ranges overlapped with the ranges of other bat and
rodent species, respectively. And though rodents experience more
range overlaps than bats (due to their greater number of
species), the effect of sympatry was almost four times stronger
for bats.

Compared with rodents, "adding one more bat species to another
bat species' range will have a greater effect on the number of
viruses it has," Luis told LiveScience. Essentially, bats share
their viruses more than rodents do, a fact that's especially
evident when one examines the number of host species each virus
has. Each bat virus, on average, infects 4.51 bat species, while
each rodent virus infects only 2.76 rodent species. This greater
sharing of viruses likely results because bats typically live in
very close quarters with millions of other bats, Luis said.
Physical and genetic similarities between different bat species
may also help the viruses spread more easily.

In addition to sympatry, certain life-history traits appear to
affect the number of viruses a bat species has. Bat species that
live longer, have greater body masses, smaller
litter sizes and more litters per year tend to host more
zoonotic viruses, the scientists found.

Public health concern?

"I think it's a very interesting study, the first of its kind,"
said Jamie Childs, azoonotic disease epidemiologist at Yale
University, who was not involved with the research. "It confirms
in many ways the importance of bats as reservoirs for viruses."

But while the study is a good first step, it "vastly
underestimated the number of viruses bats host," Childs told
LiveScience. Recent research looking at bat guano suggests there
are a number of viral agents we don't have much information on,
he said. [ Tiny
& Nasty: Images of Things That Make Us Sick ]

Underestimation or not, the study highlights the public health
concern of bat viruses, Childs said. Though humans don't often
come into direct contact with bats, they can catch their viruses
through contact with infected domesticated animals, including
horses, cattle and cats. The majority of human rabies outbreaks
have been linked back to bats, and transmission of the Nipah and
Hendra viruses have resulted in large outbreaks with lots of
fatalities, he said. Even outbreaks of the Ebola and Marburg
viruses, which don't often kill a lot of people, catch the
attention of the worldwide community.

But is there anything we can do to prevent future outbreaks of
bat viruses?

Childs doesn't think so, given how the infections spread and the
number of different species the viruses can jump to. "It's very
hard to control the emergence of these infections with humans,"
he said.

Hayman, on the other hand, thinks that studying the interactions
between bats, humans and domestic animals could be helpful. "We
should to be looking at what we are doing to make bats come into
contact with humans and domestic animals, and try to mitigate
that," he said.

The study was published online recently in the journal
Proceedings of the Royal Society B.